The present invention relates to an adjunct arrangement for a telecommunication device to be coupled between a telecommunication network supporting voice and data services and the telecommunication device, which adjunct arrangement comprises switching means for switching the telecommunication device between a mute mode and a voice mode, whereby the data service is supported when the telecommunication device is in the mute mode.
Adjunct arrangements of this kind are known. Such a known adjunct arrangement is coupled between a telecommunication network such as an analog public switched telephone network and a telecommunication device such an ordinary analog telephone set for voice communication with the network and is used for suppressing the speech from the network to the telephone set and vice versa, when the data services have to be supported during a voice communication. In this so-called mute mode, the adjunct arrangement can exchange data signals with the telecommunication network. The voice communication is only interrupted for short periods of time, typically five seconds at most each time when the voice communication is interrupted. The data service is thus provided in the form of so-called off-hook signalling. Network operators impose requirements upon such off-hook signalling, both hardware requirements such as network termination requirements and software requirements such as network protocol requirements. A typical data service implemented by means of off-hook signalling is a call waiting service provided to a party trying to call a party being in a voice communication with another party. During such a call waiting service, the network sends a call alert signal in the form of a short tone to the party whose call is intruded. Thereupon, the telephone set of this party is muted and the set sends an acknowledge signal to the network supporting the call waiting service. The network may then send a short data stream to the adjunct arrangement of the party whose call is intruded so as to inform this party of the identity of the intruding party. Also other services can be provided. When using an adjunct arrangement for muting a voice communication so as to exchange data, at least some of several requirements have to be met. Usually analog telephone sets have no own DC-supply but get their DC-supply from the network. The adjunct arrangement has a separate DC-supply, preferably a battery. When the separate DC-supply fails, the default settings of the adjunct arrangement should be such that the telephone set is still able to fulfill its voice communication task. When the adjunct arrangement is switched into the mute mode, electrically the telephone set should see as few changes as possible. Furthermore, the adjunct arrangement must meet network operator's requirements such as the FCC part 68 requirements in the USA or similar requirements elsewhere. Also, when in mute mode, the muting should be as good as possible, or should at least fulfill local requirements such as the Bellcore SR-3004 requirements as to attenuation. Although known adjunct arrangements could meet the above requirements, such known adjunct arrangements have disadvantages. In one known adjunct arrangement, in mute mode, a DC-current source supplied by the adjunct arrangement's battery is switched parallel to the telephone set, a termination impedance matching the set's impedance being switched parallel to the current source, whereas a gyrator circuit is switched across the network's terminals. In the known adjunct arrangement mode switching is done by means of a relay also requiring supply from the adjunct arrangement's battery. The battery of such an adjunct arrangement will be exhausted quickly so that the adjunct arrangement is impractical when used. Furthermore, because of the relatively high line-voltage that has to be supplied to the telephone set when in mute-mode, the DC-supply is complicated and expensive.